Building on this, my understanding is that a home's A/C power is delivered via a charged line into the main breaker box. All of the electrical devices in the home are powered from this line. The breaker box is grounded using an earth ground, which is just a copper line running X feet deep into the ground (usually using the plumbing system).Your basic understanding is flawed. You need to know that there are at least three different kinds of "ground" and you have to discern which one is being referred to by context.
Types of "ground":
1) The literal planet Earth. This is an RF ground for antennas and lightning. The utility uses it as a circuit conductor sometimes. Probably shouldn't though.
2) The point in the circuit considered 0 volts. This is not a constant of nature. This "ground" might not even be connected to the planet. It is artificial and arbitrary. Consider the negative battery terminal in a vehicle. It is universally called "ground". Maybe even called "common" in some fields. This ground carries a current.
3) Equipment ground. This is the conductor connected to the source such that a path for short circuits and stray leaks is created. It isn't normally a "live" conductor.
Electricity flows from a point of high potential to low potential like a ball rolling down a hill. Electrons are not gained or lost by the circuit. The electrons in the entire circuit is constant. They move around the complete path from generator to load and back in a closed loop. It's like an escaltor to a water slide. You ride the escaltor up, gaining potential, and slide back down, releasing the stored energy and and up back at the bottom of the escalator to do it all again.
Every electron that leaves a battery or generator comes back to it.
What I'm struggling with here is that there is no return ground going back to the power plant, so I'm failing to see how the electrons are returning to the source.